FinFET with dummy fins and methods of making the same

ABSTRACT

A semiconductor structure includes semiconductor fins protruding out of a substrate, dielectric fins protruding out of the substrate and disposed among the semiconductor fins, and gate stacks disposed over the semiconductor fins and the dielectric fins. The dielectric fins include a first dielectric material layer, a second dielectric material layer disposed over the first dielectric material layer, and a third dielectric material layer disposed over the second dielectric material layer, where the first and second dielectric material layers have different compositions and the first and the third dielectric material layers have the same compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/733,188 filed on Sep. 19, 2018, the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometric size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed.

For example, a three-dimensional transistor, such as a fin-likefield-effect transistor (FinFET), has been introduced to replace aplanar transistor. A typical FinFET is fabricated with a thin “fin” (orfin structure) extending up from a substrate. The channel of the FET isformed in this vertical fin, and a gate is formed over (e.g., wrappingaround) the channel region of the fin. While existing FinFET fabricationtechniques have been generally adequate, they have not been entirelysatisfactory in all aspects. Therefore, in order to continue to meetever-increasing design requirements for FinFET devices at increasedfunctional density and decreased geometric sizes, further advances areneeded.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a perspective view of a semiconductor structure, constructedin accordance with some embodiments of the present disclosure.

FIG. 1B is a planar top view of the semiconductor structure of FIG. 1A,constructed in accordance with some embodiments of the presentdisclosure.

FIG. 1C is a cross-sectional view of the semiconductor structure of FIG.1A taken along the dashed line AA′, constructed in accordance with someembodiments of the present disclosure.

FIG. 1D is a cross-sectional view of the semiconductor structure of FIG.1A taken along the dashed line BB′, constructed in accordance with someembodiments of the present disclosure.

FIG. 1E is a cross-sectional view of the semiconductor structure of FIG.1A taken along the dashed line CC′, constructed in accordance with someembodiments of the present disclosure.

FIGS. 2A and 2B illustrate a flowchart of an integrated circuitfabrication method in accordance with some embodiments of the presentdisclosure.

FIG. 3 is a perspective view of a semiconductor structure, constructedin accordance with some embodiments of the present disclosure.

FIGS. 4A, 5A, 6A, 7A, 8A, 9A, 11A, 12A, 13A, 14A, and 15A areperspective views of the semiconductor structure at various fabricationstages of a method, constructed in accordance with some embodiments ofthe present disclosure.

FIGS. 4B, 5B, 6B, 7B, 8B, 9B, 11B, 12B, 13B, 14B, and 15B are top viewsof the semiconductor structure of FIGS. 4A, 5A, 6A, 7A, 8A, 9A, 11A,12A, 13A, 14A, and 15A, respectively, constructed in accordance withsome embodiments of the present disclosure.

FIG. 10A is a top view of the semiconductor structure at an intermediatefabrication state of a method, constructed in accordance with someembodiments of the present disclosure.

FIGS. 4C, 5C, 6C, 7C, 8C, 9C, 10B, 11C, 12C, 13C, 14C, and 15C arecross-sectional views of the semiconductor structure taken along thedashed line AA′ of FIGS. 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A,14A, and 15A, respectively, constructed in accordance with someembodiments of the present disclosure.

FIGS. 4D, 5D, 6D, 7D, 8D, 9D, 10C, 11D, 12D, 13D, 14D, and 15D arecross-sectional views of the semiconductor structure taken along thedashed line BB′ of FIGS. 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A,14A, and 15A, respectively, constructed in accordance with someembodiments of the present disclosure.

FIG. 15E is a cross-sectional view of the semiconductor structure ofFIG. 15A taken along the dashed line CC′, constructed in accordance withsome embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features. Still further, when anumber or a range of numbers is described with “about,” “approximate,”and the like, the term is intended to encompass numbers that are withina reasonable range including the number described, such as within +/−10%of the number described or other values as understood by person skilledin the art. For example, the term “about 5 nm” encompasses the dimensionrange from 4.5 nm to 5.5 nm.

The present disclosure is directed to, but not otherwise limited to, afin-like field-effect transistor (FinFET) device. The FinFET device, forexample, may be a complementary metal-oxide-semiconductor (CMOS) deviceincluding a p-type metal-oxide-semiconductor (PMOS) FinFET device and ann-type metal-oxide-semiconductor (NMOS) FinFET device. The followingdisclosure will continue with a FinFET example to illustrate variousembodiments of the present invention. In particular, the presentdisclosure may be equally applicable to device FinFET logic devices andFinFET memory devices (e.g., static random-access memory, or SRAM). Itis understood, however, that the application should not be limited to aparticular type of device, except as specifically claimed.

FIG. 1A is a perspective view of a portion of a workpiece 100 accordingto various aspects of the present disclosure. FIG. 1B is a planar topview of the workpiece 100. FIGS. 1C, 1D, and 1E are cross-sectionalviews of the workpiece 100 along the dashed lines AA′, BB′, and CC′,respectively, constructed according to various aspects of the presentdisclosure. FIGS. 1A-1E have been simplified for the sake of clarity andto better illustrate the concepts of the present disclosure. Additionalfeatures may be incorporated into the workpiece 100, and some of thefeatures described below may be replaced or eliminated for otherembodiments of the workpiece 100.

The workpiece 100 includes a substrate 102. The substrate 102 mayinclude an elementary (single element) semiconductor, such as siliconand/or germanium; a compound semiconductor, such as silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor such as SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; and/or other suitablesemiconductor materials. The substrate 102 may be a single-layermaterial having a uniform composition. Alternatively, the substrate 102may include multiple material layers having similar or differentcompositions suitable for IC device manufacturing. In one example, thesubstrate 102 may be a silicon-on-insulator (SOI) substrate having asemiconductor silicon layer formed on a silicon oxide layer.

The workpiece 100 also includes various isolation features 128 andactive regions 106 defined by the isolation features 128. The isolationfeatures 128 may include any suitable materials, such as silicon oxide,silicon nitride, silicon oxynitride, fluoride-doped silicate glass(FSG), a low-k dielectric material, and/or other suitable insulatingmaterial. The isolation features 128 may be shallow trench isolation(STI) features. Other isolation features such as field oxide, LOCaloxidation of silicon (LOCOS), and/or other suitable features may also beimplemented as the isolation features 128. The isolation features 128may include a multi-layer structure, for example, having one or morethermal oxide liner layers. In the depicted embodiment, the isolationfeatures 128 include an oxygen-containing dielectric material, such assilicon oxide.

In some embodiments, the active regions 106 having a non-planarstructure extend upward to above the isolation features 128, whichinclude a dielectric layer 112. The active regions 106 are hereafterreferred to as semiconductor fins 106, to be differentiated fromdielectric fins 118B-118E and hybrid fins 110 to be introduced below.Multiple semiconductor fins 106 are together referred to as asemiconductor fin structure. While the illustrated embodiments includesuch a fin structure, further embodiments may include other raisedactive and passive devices formed upon the substrate 102. Thesemiconductor fins 106 protrude out of the substrate 102 and extend awayfrom the isolation features 128 along the Z direction. Furthermore, thesemiconductor fins 106 are oriented lengthwise along the Y direction andare spaced from each other along the X direction. In the depictedembodiment, the X, Y, and Z directions are orthogonal to each other.

In the present embodiment, referring collectively to FIGS. 1A-1E, theworkpiece 100 includes various FETs designed for various functions, suchas core devices, memory devices, input/output (I/O) devices, othersuitable devices, or combinations thereof. An example FET 152 isillustrated by a dashed circle in FIG. 1A to include various features ofthe FET, the formation of which will be discussed in detail below. Inmany embodiments, the FET 152 includes epitaxial source/drain (S/D)features 136, which may include various doped semiconductor materials, ametal gate stack 146 (e.g., one of metal gate stacks 146A-146E), and achannel region 154 (as a portion of the semiconductor fin 106) disposedbetween the epitaxial S/D features 136 and under the metal gate stack146. The workpiece 100 may include multiple metal gate stacks 146oriented lengthwise along the X direction and spaced from each otheralong the Y direction. Each metal gate stack 146 may include one or moregate cut feature 148 configured to isolate adjacent gate structures toform individual FETs. The workpiece 100 may further include S/D contactfeatures 150 disposed over the epitaxial S/D features 136. Variousfeatures (e.g. FETs 152) of the workpiece 100 are separated by anetch-stop layer (e.g., an etch-stop layer) 142 and an interlayerdielectric (ILD) layer 140.

The workpiece 100 further includes dielectric fins 118B-118E, orcollectively referred to as a dielectric fin structure 118. Similar tothe semiconductor fins 106, the dielectric fin structure 118 extend awayfrom the isolation features 128 along the direction Z, though they aredielectric (e.g., insulating or inactive) features disposed between thesemiconductor fins 106. The dielectric fin structure 118 of the presentdisclosure have various dimensions and orientations. For example, thedielectric fins 118B-118D oriented lengthwise along the Y direction(i.e., substantially parallel to the orientation of the semiconductorfins 106) have different widths. As depicted herein, a width W₁ of thedielectric fin 118B is less than a width W₂ of the dielectric fin 118C,which is less than a width W₃ of the dielectric fin 118D. In someembodiments, a ratio of W₃ to W₂ is from about 1 to about 4. In someembodiments, W₁ is similar to a width W_(f) of the semiconductor fin106. The dielectric fin structure 118 may also include a dielectric fin118E oriented lengthwise along the X direction (i.e., substantiallyorthogonal to the dielectric fins 118B-118D) that is substantiallysimilar in width as the dielectric fin 118D. In some examples, W_(f) andW₁ may be from about 5 nm to about 15 nm, W₂ may be from about 20 nm toabout 50 nm, and W₃ may be from about 50 nm to about 200 nm. Of course,other dimensions of the semiconductor fin 106 and the dielectric fins118B-118D may also be applicable in the present disclosure.

The dielectric fins 118B-11E, with their respective dimensions andlocations, are configured to support the overall structure of theworkpiece 100 in many aspects. Due to various design and processingparameters, the density of the semiconductor fins 106 formed over thesubstrate 102 may not be uniform, i.e., some portions of the workpiece100 may include a greater density of semiconductor fins 106 than otherportions. Furthermore, many semiconductor fins 106 may be truncatedduring fabrication, further altering the density of the semiconductorfins 106 in some portions of the workpiece 100. As a result, when gatestructures (e.g., dummy gate stacks 130A-130E to be described in detailbelow) are subsequently formed over the semiconductor fins 106, thoseportions of the workpiece 100 having a lower density of thesemiconductor fins 106 may not provide sufficient structural support forthe gate structures, leading to collapse or bending of the gatestructures. Additionally, during a cut metal gate (CMG) processperformed on replaced metal gate stacks (e.g., metal gate stacks146A-146E) to form gate cut features 148, damage to the workpiece 100may occur as a result of unintentional lateral over-etching of twoneighboring semiconductor fins 106 in close proximity. For at leastthese reasons, the present disclosure provides embodiments in which thedielectric fins 118B-118E are configured to at least provide structuralsupport for subsequently formed gate structures (e.g., dummy gate stacks130A-130E) in areas where semiconductor fins 106 are absent (referringto the dielectric fins 118B-118D depicted in FIGS. 1A-1E), tune theoverall fin density, enlarge the processing window for forming the gatecut features 148 (referring to the gate cut features 148 formed over thedielectric fins 118-118D as depicted in FIG. 1E), and enhance themechanical strength of the semiconductor fins 106.

The dielectric fins 118B-118E may include a single dielectric materiallayer, such as dielectric material layer 120 (e.g., the dielectric fins118B and 118C), or multiple dielectric material layers, such asdielectric material layers 120, 122, and/or 124 (e.g., the dielectricfins 118D and 118E). In the depicted embodiment, the narrower dielectricfins 118B and 118C may include a single dielectric material layer, suchas the dielectric material layer 120. In furtherance to the depictedembodiment, the wider dielectric fins 118D and 118E may include multipledielectric material layers, where the dielectric material layer 124 isdisposed over the dielectric material layer 122, which is disposed overthe dielectric material layer 120. In the depicted embodiment, thedielectric material layer 120 wraps around the dielectric materiallayers 122 and 124. In other words, sidewalls of the dielectric materiallayer 120 are in direct contact with sidewalls of both the dielectricmaterial layers 122 and 124. Notably, referring to FIGS. 1C and 1D, awidth W₄ of the dielectric material layer 122 is similar to orsubstantially the same as a width W₅ of the dielectric material layer124 and less than W₃. Stated another way, W₄ and W₅ both span from onesidewall of the dielectric material layer 120 to another. In someembodiments, a ratio of W₄ (or W₅) to W₃ is from about 0.6 to about 0.9.In some examples, W₄ and W₅ may be from about 30 nm to about 180 nm, andW₃ may be from about 50 nm to about 200 nm. Further, the dielectricmaterial layer 120 is configured to contact a bottom surface of thedielectric material layer 122 and sidewalls of the dielectric materiallayers 122 and 124.

In many embodiments, the dielectric material layer 120 is similar to thedielectric material layer 124 in composition and may both include anitrogen-containing dielectric material, such as silicon nitride, ametal-containing nitride, other suitable materials, or combinationsthereof. In some examples, a difference in the composition of nitrogenbetween the dielectric material layer 120 and the dielectric materiallayer 124 is no more than about 2% (atomic percent). The dielectricmaterial layer 122 is different from the dielectric material layers 120and/or 124 in composition and may include an oxygen-containingdielectric material, such as silicon oxide, silicon oxycarbide, siliconcarbon oxynitride, other suitable materials, or combinations thereof.Notably, the dielectric material layer 122 is similar to the dielectriclayer 112 (i.e., isolation features 128) in composition as they bothinclude an oxygen-containing dielectric material. In some examples, adifference in the composition of oxygen between the dielectric materiallayer 122 and the dielectric layer 112 is no more than about 2% (atomicpercent). Furthermore, as will be discussed in detail below, methods offorming the dielectric material layers 120, 122, and 124 may differ aswell. By using multiple dielectric material layers to form thedielectric fins 118D and 118E, the processing capability is increased.For example, after the filling of the dielectric material layer 120, theaspect ratios of the trenches are reduced, making them easier to befilled with a subsequent dielectric material layer (e.g., the dielectricmaterial layer 122). As a result, the processing window of forming thedielectric fins 118D and 118E is enhanced, the detail of which will befurther explained below. Furthermore, by including different dielectricmaterials, etching selectivity between the dielectric fins and theisolation features 128 may be enhanced, improving the processingcapability.

The dielectric fins 118B-118E may be formed by any suitable method, suchas atomic layer deposition (ALD), chemical vapor deposition (CVD),flowable CVD (FCVD), spin-on coating, physical vapor deposition (PVD),other suitable methods, or combinations thereof. In the depictedembodiment, the dielectric material layers 120 and 124 are formed by anALD process, while the dielectric material layer 122 is formed by anFCVD and/or a spin-on coating process. The fabrication of the dielectricfin structure 118 will be discussed in detail below.

The workpiece 100 further includes hybrid fins 110 that each includes asemiconductor portion 110A as depicted in FIG. 1C and a dielectricportion 110B as depicted in FIG. 1D. The semiconductor portion 110A andthe dielectric portion 110B are oriented along the direction Y (i.e.,substantially parallel to the semiconductor fins 106 and the dielectricfins 118B-118D), such that sidewalls of the semiconductor portion 110Aand sidewalls of the dielectric portion 110B are continuous along thedirection Y. In some embodiments, sidewalls of the semiconductor portion110A are coplanar with sidewalls of the dielectric portion 110B alongthe direction Y. In many embodiments, the dielectric portion 110B isdisposed under the metal gate stack 146 (e.g., 146B as depicted in FIG.1A). The semiconductor portion 110A is similar to the semiconductor fins106 in composition, while the dielectric portion 110B includes thedielectric material layer 124. In the depicted embodiment, anothersemiconductor portion 110C having a height H is disposed under thedielectric portion 110B along the Z direction. In other words, a bottomsurface of the dielectric portion 110B is in contact with a top surfaceof the semiconductor portion 110C. In further embodiments, the bottomsurface of the dielectric portion 110B is below a bottom surface of thedielectric fins 118B-118D. In one example, H is greater than 0 and maybe less than about 20% a height of the hybrid fins 110. In otherembodiments, the semiconductor portion 110C is omitted from theworkpiece 100, such that the bottom surface of the dielectric portion110B is in direct contact with a top surface of the substrate 102. Incontrast, bottom surface of the dielectric fins 118B-118D are separatedfrom the substrate 102 by the isolation features 128.

When forming gate structures (e.g., dummy gate stacks 130A-130E),misalignment between the gate structures and the semiconductor may causestructural defects (e.g., voids) to form in the semiconductor fin,especially during subsequent processes of forming sour/drain features.In some embodiments of the present disclosure, replacing a portion ofthe semiconductor fin with a dielectric material in a region where thegate structures are to be formed helps mitigate any potential structuraldefects introduced by the misalignment between the gate structures andthe semiconductor fins. The dielectric portion 110B of the hybrid fins110 as discussed above is configured to mitigate the potential effectsof misalignment in gate structures.

Methods of forming the workpiece 100 having FETs 152 will now bedescribed with reference to FIGS. 2A-15D. FIGS. 2A-2B illustrate aflowchart of a method 200 for fabricating the workpiece 100 according tovarious aspects of the present disclosure. The figures that follow referperspective views, top views, and cross-sectional views of the workpiece100 taken through the source/drain regions (e.g., along the dashed lineAA′) or through the metal gate stacks 146 (e.g., along the dashed lineBB′) of the workpiece 100.

The method 200 and the structure of the workpiece 100 are collectivelydescribed according to various aspects of the present disclosure. It isunderstood that additional steps can be provided before, during, andafter the method 200 and that some of the steps described can bereplaced or eliminated for other embodiments of the method. In thefollowing description, the active regions are also referred to assemiconductor fins 106.

Referring to FIG. 2A and to FIG. 3, the method 200 at operation 202provides (or is provided with) a workpiece 100, which includes asubstrate 102 as described in detail above. The substrate 102 may beuniform in composition or may include various layers. The layers mayhave similar or different compositions, and in various embodiments, somesubstrate layers have non-uniform compositions to induce device strainand thereby tune device performance. Examples of layered substratesinclude silicon-on-insulator (SOI) substrates. In some such examples,the substrate 102 may include an embedded insulating layer such as asilicon oxide, a silicon nitride, a silicon oxynitride, or othersuitable insulating materials.

The substrate 102 may have one or more layers formed upon it. Forexample, the substrate 102 includes one or more semiconductor layerepitaxially grown on bulk silicon, such as a silicon wafer. For example,the substrate 102 includes a first semiconductor layer formed on bulksilicon and a second semiconductor layer formed on the firstsemiconductor layer. The first semiconductor layer includes a firstsemiconductor material (such as SiGe) and the second semiconductor layerincludes a second semiconductor material (such as Si) different from thefirst semiconductor material. The first and second semiconductor layersare epitaxially grown by suitable techniques, such as selective epitaxygrowth (SEG). In some embodiments, suitable deposition processes forepitaxy growth include atomic layer deposition (ALD), chemical vapordeposition (CVD), physical vapor deposition (PVD), high-density plasmaCVD (HDP-CVD), and/or other suitable deposition processes. Any of thesetechniques may be used to grow the semiconductor layer having anycomposition including a graded composition. In some embodiments, thesubstrate 102 may be doped by a proper method, such as ion implantation.

To facilitate fabrication and to avoid damage to the semiconductorlayer, one or more hard mask layer 104 may be formed on the substrate102. For example, the hard mask layer 104 may include a dielectric suchas semiconductor oxide, semiconductor nitride, semiconductor oxynitride,or semiconductor carbide. In some examples, the hard mask layer 104includes two or more films stacked together, such as a silicon oxidefilm and a silicon nitride film in stack. The hard mask layer 104 may beformed by thermal growth, ALD, CVD, HDP-CVD, PVD, and/or other suitabledeposition processes. The hard mask may include other suitable material,such as a silicon oxide layer and a poly-silicon layer on the siliconoxide layer.

Referring to FIG. 2A and to FIGS. 4A-4D, the method 200 at operation 204patterns the substrate 102 to form one or more semiconductor fins 106extending away from the substrate 102. In some embodiments, theoperation 204 includes one or more lithography and etching processes. Infurther embodiments, the operation 204 includes forming a patternedresist layer (e.g., photoresist layer; not depicted) and forming a finstructure that includes one or more semiconductor fins 106 separated bytrenches 108 using the patterned resist layer as an etch mask. In thepresent embodiment, the openings in the patterned resist layer are firsttransferred to the hard mask layer 104 by an etching process and thentransferred to the substrate 102 by one or more subsequent etchingprocess. More details of the operation 204 are further provided below.

The resist layer used to form the semiconductor fins 106 may be formedon the hard mask layer 104. An example resist layer includes aphotosensitive material that undergoes a property change when exposed tolight, such as ultraviolet (UV) light, deep UV (DUV) light or extreme UV(EUV) light. This property change can be used to selectively removeexposed or unexposed portions of the resist layer by a developingprocess. This procedure to form a patterned resist layer is alsoreferred to as a lithographic patterning or lithography process.

In one embodiment, the resist layer is patterned to leave the portionsof the photoresist material disposed over the workpiece 100 by thelithography process. After patterning the resist, an etching process isperformed on the workpiece 100 to open the hard mask layer 104, therebytransferring the pattern from the resist layer to the hard mask layer104. The remaining resist layer may be removed after the patterning thehard mask layer 104. An exemplary lithography process includes spin-oncoating a resist layer, soft baking of the resist layer, mask aligning,exposing, post-exposure baking, developing the resist layer, rinsing,and drying (e.g., hard baking). Alternatively, a lithographic processmay be implemented, supplemented, or replaced by other methods such asmaskless photolithography, electron-beam writing, and ion-beam writing.The etching process to pattern the hard mask layer may include wetetching, dry etching or a combination thereof. The first etching processapplied to the hard mask layer 104 may include multiple etching steps.For example, the silicon oxide film in the hard mask layer may be etchedby a diluted hydrofluorine solution and the silicon nitride film in thehard mask layer may be etched by a phosphoric acid solution. The secondetching process applied to the substrate 102 may include any suitableetching technique such as dry etching, wet etching, other etchingmethods (e.g., reactive ion etching (RIE)), or a combination thereof. Insome examples, the second etching process may include multiple etchingsteps with different etching chemistries, each targeting a particularmaterial of the workpiece 100. In some examples, the semiconductormaterial of the substrate 102 may be etched by a dry etching processusing a fluorine-based etchant. In some embodiments, etching includesmultiple etching steps with different etching chemistries, eachtargeting a particular material of the substrate 102 and each selectedto resist etching the hard mask layer 104. For example, a dry etchingprocess may implement an oxygen-containing gas, a fluorine-containinggas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containinggas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃), a bromine-containing gas(e.g., HBr and/or CHBR₃), an iodine-containing gas, other suitable gasesand/or plasmas, and/or combinations thereof. For example, a wet etchingprocess may comprise etching in diluted hydrofluoric acid (DHF);potassium hydroxide (KOH) solution; ammonia; a solution containinghydrofluoric acid (HF), nitric acid (HNO₃), and/or acetic acid(CH₃COOH); or other suitable wet etchant. The remaining portions of thesemiconductor layers become the semiconductor fins 106, defining thetrenches 108 (e.g., trenches 108B-108D) between the semiconductor fins106.

Numerous other embodiments of methods to form the semiconductor fins 106may be suitable. For example, the semiconductor fins 106 may bepatterned using double-patterning or multi-patterning processes.Generally, double-patterning or multi-patterning processes combinephotolithography and self-aligned processes, allowing patterns to becreated that have, for example, pitches smaller than what is otherwiseobtainable using a single, direct photolithography process. For example,in one embodiment, a sacrificial layer is formed over a substrate andpatterned using a photolithography process. Spacers are formed alongsidethe patterned sacrificial layer using a self-aligned process. Thesacrificial layer is then removed, and the remaining spacers, ormandrels, may then be used to pattern the semiconductor fins 106.

The patterning (e.g., lithography and etching) processes are configuredto produce semiconductor fins 106 of any suitable height and widthextending from the substrate 102. Particularly, the etching processapplied to the substrate 102 is controlled such that the substrate 102is partially etched, as illustrated in FIG. 4A. This may be achieved bycontrolling etching time or by controlling other etching parameter(s).By the etching processes, the semiconductor fins 106 are formed toextend away from the substrate 102. The workpiece 100 includes a finstructure of multiple semiconductor fins 106 oriented lengthwise in theY direction. In addition to forming the semiconductor fins 106, thepatterning process also defines one or more trenches 108A, 108B, 108C,and 108D (or collectively referred to as the trenches 108) between thesemiconductor fins 106. As discussed above, the semiconductor fins 106each include one or more semiconductor material the same as or differentform that of the substrate 102. For example, the semiconductor fins 106each include silicon, germanium, silicon germanium, or other suitablesemiconductor material. In other examples, the semiconductor fins 106include silicon germanium with a graded concentration, such as thegermanium concentration increasing toward the top surface of thesemiconductor fins.

Referring to FIG. 2A and to FIGS. 5A-5D, the method 200 at operation 206proceeds to form the dielectric layer 112 on the substrate 102. In thepresent embodiment, the dielectric layer 112 is deposited on thesubstrate 102 with a conformal profile, covering the substrate 102 andover sidewalls and top surfaces of the semiconductor fins 106. Thedielectric layer 112 may include a single dielectric material layer ormultiple dielectric material layers. Suitable dielectric materials forthe dielectric layer 112 include silicon oxides, silicon nitrides,silicon carbides, FSG, low-k dielectric materials, field oxide, LOCOS,other suitable dielectric materials, or a combination thereof. Thedielectric material may be deposited by any suitable technique includingthermal growth, ALD, CVD, HDP-CVD, PVD, and/or spin-on techniques. Inthe illustrated embodiment, an ALD process is used as the conformaldeposition technique for forming the dielectric layer 112. Thedielectric layer 112 constitutes, at least partially, isolation features128 as discussed with reference to FIGS. 1A-1D, such as a shallow trenchisolation feature (STI).

As will be shown below at a later stage of the method 200, thedielectric fins 118B-118D will be formed in at least some of thetrenches (e.g., in the trenches 108B, 108C, and 108D, etc.). Incontrast, some trenches between the semiconductor fins 106 withrelatively narrower spacing (e.g., less than about 2 nm) may be filledup by the dielectric layer 112, such as the trench 108A, and thus nodielectric fin is formed in these trenches. In the depicted embodiment,some trenches may have a width substantially similar to a width W_(f) ofthe semiconductor fin 106, such as the trench 108B. Some trenchesbetween semiconductor fins 106 with relatively wider spacing may havegaps larger than W_(f), such as the trenches 108C or 108D.

Referring to FIG. 2A and to FIGS. 6A-6D, the method 200 at operation 208proceeds to form a course cut (or cut trench) 108E to the semiconductorfins 106 by one or more lithography and etching processes. The cuttrench 108E is a trench cut through the semiconductor fins 106, definingends of the semiconductor fins 106. The cut trench 108E extends throughmultiple semiconductor fins 106 along the X direction. The lithographyand etching processes implemented at the operation 208 are similar tothose implemented at the operation 204. Particularly, a patterned resistlayer (not depicted) is formed by a lithography patterning process, andan etching process is applied to the semiconductor fins 106 and thedielectric layer 112 to form the cut trench 108E using the patternedresist layer as an etch mask. The cut trench 108E's width W_(c) issubstantially greater than the width W_(f) of the semiconductor fins106. In some embodiments, the width W_(c) may be different from thewidths of other trenches (e.g., 108B-108D) because it is defined by aseparate patterning process at operation 208 and is configured fordifferent design criteria (e.g., enough spacing between adjacent finends and/or mitigates unintentional over-etching of the semiconductorfins 106 during a CMG process as discussed above). After the formationof the cut trench 108E, the patterned resist layer is removed by wetstripping or plasma ashing. In some embodiments, the cut trench 108E maybe omitted from the workpiece 100.

Referring to FIG. 2A and to FIGS. 7A-7D, the method 200 proceeds atoperation 210 to fill or partially fill the trenches 108 between thesemiconductor fins 106 with the dielectric material layer 120. In manyembodiments, the dielectric material layer 120 includes anitride-containing material, such as silicon nitride or a metal nitride(e.g., aluminum nitride), other suitable dielectric materials, orcombinations thereof. In the depicted embodiment, the trenches 108B and108C are completely filled with the dielectric material layer 120 toform dielectric fins 118B and 118C, respectively, while the trenches108D and 108E are partially filled with the dielectric material layer120. As discussed above, the trenches 108 have varying dimensions. Thedielectric material layer 120 may be deposited conformally in thetrenches 108 by any suitable method such as ALD, CVD, PVD, othersuitable methods, or combinations thereof. In the depicted embodiment,the dielectric material layer 120 is formed by an ALD process. Asdescribed in detail below, the trenches 108D and 108E further includeadditional dielectric material layers.

Referring to FIG. 2A and to FIGS. 8A-8D, the method 200 at operation 212completely fills the trenches 108D and 108E with the dielectric materiallayer 122 to form the dielectric fins 118D and 118E, respectively. Thedielectric material layer 122 is different from the dielectric materiallayer 120 in composition. For examples, the dielectric material layer120 includes a nitride-containing dielectric material, while thedielectric material layer 122 includes an oxide-containing dielectricmaterial, such as silicon oxide, silicon oxycarbide, silicon carbonoxynitride, metal oxide (e.g., aluminum oxide), other dielectricmaterials, or combinations thereof. The dielectric material layer 122may be deposited by flowable CVD (FCVD) or spin-on deposition ratherthan ALD, because FCVD (or spin-on deposition) offers more efficientfilling of the trenches 108D and 108E with an oxide-containing materialcompared to the ALD process used to deposit the dielectric materiallayer 120.

Thereafter, still referring to FIG. 2A and FIGS. 8A-8D, the method 200at operation 212 proceeds to perform a polishing process, such as achemical mechanic polishing (CMP) process, to planarize a top surface ofthe workpiece 100 and to remove any excessive portions of the dielectricmaterial layer 122. In some embodiments, the hard mask layer 104 mayfunction as a CMP stop layer. In some embodiments, the hard mask layer104 may be removed by the CMP process or an additional etching process.In the depicted embodiment, the CMP process stops above the hard masklayer 104, such that a portion of the dielectric material layer 122remains over the hard mask layer 104.

Referring to FIG. 2A and to FIGS. 9A-9D, the method 200 at operation 214removes portions of the dielectric material layer 122 to form a recess125 in the dielectric fins 118D and 118E. In other words, the dielectricfins 118D and 118E are partially recessed at operation 214 by an etchingprocess. The etching process may be a dry etching process, a wet etchingprocess, an RIE process, other etching processes, or combinationsthereof. In an example embodiment, the etching process is a dry etchingprocess implementing one or more fluorine-containing orchlorine-containing gas. In the depicted embodiment, because thedielectric material layer 120 and the dielectric material layer 122differ in composition, the method 200 may remove the portions of thedielectric material layer 122 by, for example, a selective etchingprocess. The etching process may be tuned to remove the dielectricmaterial layer 122 at a greater rate than the dielectric material layer120, such that a top surface of the dielectric material layer 122 isbelow a top surface of the dielectric material layer 120 after themethod 200 performs the operation 214. In one example, about 30% of thedielectric material layer 122 may be removed by the etching process atoperation 214.

Referring to FIG. 2B and to FIGS. 10A-10C, the method 200 at operation216 removes portions of at least one semiconductor fin 106 along the Ydirection to form a recess 127. In the depicted embodiment, portions ofthree semiconductor fins 106 are removed by one or more lithography andetching processes similar to those described in reference to operation204. For example, a patterned resist layer (not depicted) may be formedover the workpiece 100, exposing the portions of the semiconductor fins106 to a subsequent etching process that removes portions of thesemiconductor fin 106 along the Y direction to form the recess 127.Thereafter, the patterned resist layer is removed by any suitablemethod, such as resist stripping or plasma ashing, to expose thedielectric material layer 120 and partially recessed dielectric materiallayer 122 to subsequent processing steps.

In the depicted embodiment, referring to FIGS. 10A and 10C, thesemiconductor fins 106 are partially recessed, such that portions of thesemiconductor fins 106 remain over the substrate 102 to form thesemiconductor portions 110C of the hybrid fins 110. In an exampleembodiment, a top surface of the semiconductor portions 110C is at asimilar level or below a bottom surface of the dielectric material layer120. In an alternative embodiment, the semiconductor fins 106 in therecess 127 are completely removed from the workpiece 100 (i.e., thesemiconductor portions 110C are omitted from the workpiece 100),exposing the substrate 102.

Though not depicted, in some embodiments, prior to performing thelithography and etching processes, the method 200 removes the portion ofthe dielectric material layer 120 and the dielectric layer 112 formedover the top surface of the hard mask layer 104. To do so, the method200 may first deposit a filler material (e.g., a resist material) overthe recessed dielectric material layer 122 to completely fill the recess125 and then performs a CMP process to remove the filler material, thedielectric material layer 120, and the dielectric layer 112 from the topsurface of the semiconductor fins 106, thereby exposing the hard masklayer 104. Thereafter, remaining filler material is removed by anysuitable method, such as resist stripping or plasma ashing, and themethod 200 proceeds to performing the one or more lithography andetching processes to remove portions of the semiconductor fins 106 alongthe Y direction as discussed above.

Referring to FIG. 2B and to FIGS. 11A-11D, the method 200 at operation218 deposits another dielectric material layer 124 over the workpiece100, thereby completely filling both recesses 125 and 127 to form thedielectric fins 118D and 118E. The dielectric material layer 124 may beformed by any suitable method, such as ALD, CVD, PVD, other suitablemethods, or combinations thereof. In the depicted embodiment, thedielectric material layer 124 is deposited by an ALD process. In thedepicted embodiment, the dielectric material layer 124 (i.e., thedielectric portion 110B) is formed over the top surface of thesemiconductor portion 110C. In furtherance to the depicted embodiment,the dielectric material layer 120 forms a U-shaped layer in thedielectric fins 118D and 118E, while the dielectric material layers 122and 124 fill the space within the U-shaped dielectric material layer120. In other words, the dielectric fins 118D and 118E includes threedielectric material layers, namely, the dielectric material layer 120,122, and 124, where the sidewalls of the dielectric material layer 120are in contact with the sidewalls of both of the dielectric materiallayers 122 and 124. In comparison, due to their smaller dimensions, thedielectric fins 118B and 118C include only one dielectric materiallayer, namely, the dielectric material layer 120.

Compositionally, the dielectric material layer 124 is different from thedielectric material layer 122 and the dielectric layer 112 but similarto the dielectric material 120 as discussed above. For example, thedielectric material layers 120 and 124 may both include anitrogen-containing dielectric material, such as silicon nitride, ametal-containing nitride, other suitable materials, or combinationsthereof, while the dielectric material layer 122 includes anoxygen-containing dielectric material, such as silicon oxide, siliconoxycarbide, silicon carbon oxynitride, other suitable materials, orcombinations thereof. Differences in composition between the dielectricmaterial layer 124 and the dielectric layer 112 enhances etchingselectivity between the two material layers at a subsequent processingstep.

Thereafter, still referring to FIGS. 11A-11D, the method 200 forms adielectric layer 129 over the top surface of the workpiece 100. In someembodiments, the dielectric layer 129 is configured to accommodate thesubsequent CMP process as discussed below. The dielectric layer 129 mayinclude a plasma-enhanced oxide (PEOX), plasma-enhanced SiN (PE-SiN),undoped silicate glass (USG), plasma-enhanced USG (PE-USG), othersuitable materials, or combinations thereof, and may be formed by anysuitable method such as plasma-enhanced CVD (PECVD), FCVD, othersuitable methods, or combinations thereof. In many embodiments, thedielectric layer 129 includes a composition different from that of thedielectric material layer 124 and the dielectric layer 112.

Referring to FIG. 2B and to FIGS. 12A-12D, the method 200 at operation220 performs a CMP process to remove the dielectric layer 129, portionsof the dielectric material layer 124, portions of the dielectric layer112, and the hard mask layer 104 to expose the top surface of thesemiconductor fins 106. Referring to FIGS. 12C and 12D, by planarizingthe top surface of the semiconductor fins 106, the method 200 atoperation 220 replaces portions of the semiconductor fins 106 withdielectric fins, thereby forming hybrid fins 110 having thesemiconductor portion 110A and the dielectric portion 110B arrangedadjacent to each other along the Y direction. As such, sidewalls of thesemiconductor portion 110A and the dielectric portion 110B aresubstantially continuous along the Y direction.

Referring to FIG. 2B and FIGS. 13A-13D, the method 200 at operation 222selectively recesses the dielectric layer 112 to form isolation features128. After the dielectric layer 112 is recessed, the semiconductor fins106, the dielectric fin structure 118, and the hybrid fins 110 extendabove the recessed dielectric layer 112. The semiconductor fins 106 areelectrically isolated from each other by the recessed dielectric layer112 (i.e., the isolation features 128). Any suitable etching techniquemay be used to recess the dielectric layer 112, including dry etching,wet etching, RIE, and/or other etching methods. In an exampleembodiment, an anisotropic dry etching is used to selectively remove thedielectric layer 112 at a greater rate than does the semiconductor fins106, the dielectric material layer 124, and the dielectric materiallayer 120 using a proper etchant gas, such as one or morefluorine-containing or chlorine-containing gas. The height of thesemiconductor fins 106 are determined by the etching depth of theetching process used to recess the dielectric layer 112. The etchingdepth may be determined by many factors such as, for example, etchingtime, etching bias, etching power, other factors, or combinationsthereof.

Referring to FIG. 2B and FIGS. 14A-14D, the method 200 at operation 224forms dummy gate stacks 130A-130E (collectively referred to as dummygate stacks 130). In the present embodiment, portions of the dummy gatestacks 130 will be replaced by metal gate stacks at a later fabricationstage. The dummy gate stacks 130 are formed over portions of thesemiconductor fins 106, the dielectric fins 118B-118D, and the hybridfins 110. In some examples, the formation of the dummy gate stacks 130includes depositing a gate dielectric layer 126 over the semiconductorfins 106 and the dielectric fins 118B-118D, depositing a dummy gateelectrode layer 131 containing polysilicon or other suitable materialover portions of the gate dielectric layer 126, and subsequentlypatterning the dummy gate electrode layer 131. In some embodiments, thegate dielectric layer 126 includes silicon oxide deposited conformallyby a suitable method, such as ALD, CVD, thermal oxidation, chemicaloxidation, other suitable methods, or combinations thereof. In thedepicted embodiment, the gate dielectric layer 126 is replaced with ahigh-k gate dielectric layer (not shown) during the metal gate stackreplacement process. A gate hard mask layer 132 may be formed on thedummy gate electrode layer and is used as an etch mask during thepatterning of the dummy gate electrode layer. The gate hard mask layer132 may include any suitable material, such as a silicon oxide, asilicon nitride, a silicon carbide, a silicon oxynitride, other suitablematerials, or combinations thereof. In one embodiment, the gate hardmask layer 132 includes dual mask material films 132A and 132B, such assilicon oxide and silicon nitride. In some embodiments, the patterningprocess to form the dummy gate stacks 130A-130E includes forming apatterned resist layer (not depicted) by one or more lithographyprocesses, etching the gate hard mask layer 132 using the patternedresist layer as an etch mask, and etching the dummy gate electrode layer131 to form the dummy gate stacks 130A-130E using the patterned hardmask layer 132 as an etch mask. In the depicted embodiment, one or moredummy gate stacks 130 are formed over the dielectric portion 110B of thehybrid fins 110, as shown in FIG. 14D.

In some embodiments, one or more gate spacers (not depicted) are formedon the sidewalls of the dummy gate stacks 130. The gate spacers mayinclude any suitable dielectric material, such as a semiconductor oxide,a semiconductor nitride, a semiconductor carbide, a semiconductoroxynitride, other suitable dielectric materials, or combinationsthereof. In some embodiments, the gate spacers may include multiplelayers, such as a first gate spacer (or a seal layer) on sidewalls ofthe dummy gate stacks 130A-130E and a second gate spacer on the firstgate spacer. In some embodiments, the gate spacers are formed bydeposition and anisotropic etching, such as dry etching. In one suchexample, the a spacer material is first formed over the workpiece 100 bya deposition process and anisotropically etched back to form the gatespacers along the sidewalls of the dummy gate stacks 130.

Thereafter, referring to FIG. 2B, the method 200 at operation 226 formsepitaxial S/D features 136 (see FIGS. 15A-15E) within the source/drainregions, which are defined in the semiconductor fins 106 and on bothsides of the dummy gate stacks 130. The epitaxial S/D features 136 maybe formed by selective epitaxy growth for strain effect with enhancedcarrier mobility and device performance. The dummy gate stacks 130 andgate spacer constrain the selective epitaxy growth process such that theepitaxial S/D features 136 are self-aligned in the source/drain regions.In many embodiments, the epitaxial S/D features 136 are formed by one ormore epitaxial growth (epitaxial process), whereby silicon (Si)features, silicon germanium (SiGe) features, silicon carbide (SiC)features, and/or other suitable semiconductor features are grown in acrystalline state on the semiconductor fins 106 within the source/drainregions. In an alternative embodiment, an etching process is applied torecess portions of the semiconductor fins 106 within the source/drainregions before performing the epitaxy growth. The etching process mayalso remove any dielectric material disposed on the source/drainregions, such as during the formation of the gate sidewall features.Suitable epitaxy processes include CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD),molecular beam epitaxy, and/or other suitable processes. The epitaxialS/D features 136 may be in-situ doped during the epitaxy process byintroducing doping species including: p-type dopants, such as boron orBF₂; and n-type dopants, such as phosphorus or arsenic. In an exemplaryembodiment, the epitaxial S/D features 136 in an nFET include silicondoped with phosphorous (SiP) or silicon carbide doped with phosphorous(SiCP), while those in a pFET include silicon germanium doped with boron(SiGeB), SiGeSnB (tin may be used to tune the lattice constant) and/orGeSnB. In some embodiments, the epitaxial S/D features 136 include morethan one semiconductor material layers. One or more annealing processesmay be performed thereafter to activate the epitaxial source/drainfeatures 136. Suitable annealing processes include rapid thermalannealing (RTA), laser annealing processes, other suitable annealingtechnique or a combination thereof.

Referring back to FIG. 2B, the method 200 at operation 228 replaces thedummy gate stacks 130A-130E with metal gate stacks 146A-146E(collectively referred to as metal gate stacks 146; see FIGS. 15A-15E)in a series of processes collectively referred to as “gate replacementprocess.” The gate replacement process at operation 228 begins withdepositing the ILD layer 140 over the workpiece 100, covering theisolation features 128, the epitaxial S/D features 136, the dummy gatestacks 130A-130E, and other features formed over the substrate 102. TheILD layer 140 acts as an insulator that supports and isolates conductivetraces (such as contacts, vias, and metal lines) to be formed therein.The ILD layer 140 may include any suitable dielectric material, such asa silicon oxide, low-k dielectric material, porous dielectric material,other suitable dielectric material or a combination thereof. In someembodiments, the etch-stop layer 142 is deposited over the workpiece 100before forming the ILD layer 140. The etch-stop layer 142 includes amaterial different from that of the ILD layer 140 to provide etchingselectivity. For example, the etch-stop layer 142 may include siliconnitride deposited by CVD or ALD. In some embodiments, the formation ofthe ILD layer 140 includes deposition and CMP to provide a planarizedtop surface. The gate hard mask layer 132 may be removed during the CMPprocess, an additional etching operation, or a combination thereof.

The gate replacement process at operation 228 proceeds to form metalgate stacks 146 to replace the dummy gate stacks 130. The dummy gatestacks 130A-130E are first removed by selective etching or a series ofpatterning and etching processes discussed above. The etching processmay be any suitable method, such as dry etching, wet etching, RIE,and/or other suitable methods, resulting in gate trenches (notdepicted). After the removal of the dummy gate stacks 130A-130E,materials of the metal gate stacks 146 are deposited in the gatetrenches, and a CMP process is applied to remove the excessive gatematerials and planarize the top surface.

The materials of the metal gate stacks 146 include a high-k gatedielectric layer and gate electrode (not depicted). In some embodiments,the gate dielectric layer includes a high-k dielectric material, and thegate electrode includes metal or metal alloy. The metal gate stacks 146are formed on the workpiece 100 wrapping around the channel regions 154of the semiconductor fins 106. In some examples, the high-k gatedielectric layer and the gate electrode each may include a number ofsub-layers. The high-k dielectric layer may include metal oxide, metalnitride, such as LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃(BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO,(Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), or other suitabledielectric materials. The high-k gate dielectric layer may be depositeda suitable technique, such as ALD, CVD, metal-organic CVD (MOCVD), PVD,thermal oxidation, and/or other suitable techniques. The high-k gatedielectric layer may additionally include an interfacial layer disposedbetween the semiconductor fins 106 and the high-k dielectric layer. Theinterfacial layer may include may include silicon oxide, siliconnitride, silicon oxynitride, and/or other suitable material, depositedby a suitable method, such as ALD, CVD, ozone oxidation, and/or othersuitable methods.

The gate electrode material is then deposited over the high-k gatedielectric layer in the gate trenches. The gate electrode is formed byALD, PVD, CVD, plating, other suitable process, or a combinationthereof. The gate electrode may include a single layer or multiplelayers, such as at least one work-function (WF) metal layer, a bulkconductive layer, a metal layer, a barrier layer, and/or an adhesionlayer. The gate electrode may include Ru, Cu, W, Co, Ti, Ag, Al, TiAlN,TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Mo, WN, or any suitable materials.In some embodiments, different metal materials are used for nFET andpFET devices with respective work functions. In some embodiments, then-type WF metal includes tantalum (Ta). In other embodiments, the n-typeWF metal includes titanium aluminum (TiAl), titanium aluminum nitride(TiAlN), or combinations thereof. In other embodiments, the n-metalinclude Ta, TiAl, TiAlN, tungsten nitride (WN), or combinations thereof.The n-type WF metal may include various metal-based films as a stack foroptimized device performance and processing compatibility. In someembodiments, the p-type WF metal includes titanium nitride (TiN) ortantalum nitride (TaN). In other embodiments, the p-metal include TiN,TaN, tungsten nitride (WN), titanium aluminum (TiAl), or combinationsthereof.

Referring to FIG. 2B and to FIG. 15E, the method 200 at operation 230cuts (or shortens) the metal gate stacks 146. In the present example,the metal gate stacks 146 are patterned, etched, and filled with one ormore dielectric material to form gate cut features 148. Specifically, asdiscussed above, the gate cut features 148 are formed over thedielectric fins 118B-118D, such that in the event any lateralover-etching were to occur during the CMG process, the semiconductorfins 106 adjacent the dielectric fins 118B-118D will not beunintentionally damaged by the etching process. The gate cut features148 are dielectric features to define the gate ends and the spacingbetween the gate ends. The formation of the gate cut features 148 mayinclude lithography process, etching, and deposition, and may be furtherfollowed by CMP. For examples, the formation of the gate cut featuresincludes performing a lithography process to form a patterned resistlayer with openings that define the regions for gate cut features,performing an etching process to selectively etch the gate stacksthrough the resist openings to form trenches in the gate stacks,depositing one or more dielectric material to fill in the trenches, andperforming a CMP process to remove the excessive the dielectricmaterial. The dielectric material of the gate cut features may includesilicon oxide, silicon nitride, low-k dielectric material, othersuitable dielectric material, or a combination thereof. In the depictedembodiment, the gate cut features 148 are formed in the metal gatestacks 146; however, the present disclosure is also applicable toembodiments in which the gate cut features 148 are formed in the dummygate stacks 130 before performing the gate replacement process.

Still referring to FIG. 2B and to FIGS. 15A-15D, the method 200 atoperation 232 performs additional processing steps to workpiece 100. Forexample, the method 200 forms S/D contact features 150 over theepitaxial S/D features 136. The S/D contact features 150 are conductivefeatures to electrically connect the FETs to form a functional circuit.In the present examples, the S/D contact features 150 are designed toland on epitaxial S/D features 136. The formation of the S/D contactfeatures 150 may include lithography process, etching, and deposition,and may be further followed by CMP. For examples, the formation of thecontact features includes performing a lithography process to form apatterned resist layer with openings that define the regions for contactfeatures, performing an etching process to the ILD layer 140 through theresist openings to form contact holes in the ILD layer 140, depositingone or more conductive material to fill in the contact holes, andperforming a CMP process to remove the excessive the conductivematerial. The conductive material of the contact features may include W,Cu, Co, Ru, Al, other metal or metal alloys, or a combination thereof.The S/D contact features 150 may further include a barrier layer (suchas titanium, titanium nitride, tantalum, tantalum nitride or acombination thereof) for lining the contact holes. For example, the S/Dcontact features 150 include titanium and titanium nitride as a barrierlayer deposited by CVD, ALD, or PVD, and a conductive material to fillin the contact holes by CVD, ALD, PVD, plating, other suitable techniqueor a combination thereof.

The method 200 may further include other operations during, beforeand/or after the described operations. For example, the method 200 formsother features such as interconnection features over the workpiece 100.An interconnection structure includes various conductive features toelectrically connect various devices (including FETs) to an integratedcircuit. The interconnection structure includes contact features, viafeatures and metal lines. The metal lines may be distributed in multiplemetal layers and via features vertically connect the metal lines betweenadjacent metal layers. For example, via features and metal lines mayutilize copper technologies and may be formed a damascene process, suchas dual damascene process or single damascene process.

The present disclosure provides semiconductor structures includingFinFETs and methods of making the same. In particular, embodiments ofthe present disclosure provide dielectric fins having variouscompositions and dimensions dispersed among semiconductor (i.e., active)fins for meeting different design requirements and addressing challengesarising from fabricating FinFET devices. Embodiments of the presentdisclosure provide many advantages. For example, in some embodiments,dielectric fins are formed substantially parallel to semiconductor finsto provide structural support for subsequently formed gate stacks (e.g.,metal gate stacks) that may be prone to collapsing in areas wheresemiconductor fins are sparse or absent. In some examples, such as whenfabricating FinFET SRAM devices according to embodiments of the presentdisclosure, density of fins may range from about 40% to about 70%. Insome embodiments, dielectric fins are formed substantially perpendicularto semiconductor fins for mitigating potential damage to semiconductorfins during a cut metal gate process. In some embodiments, hybrid finsincluding both a semiconductor portion and a dielectric portion areformed substantially parallel to semiconductor fins near and/or underthe gate stacks to compensate for possible misalignment (e.g., undesiredshift) of metal gate stacks that could lead to structural defects suchas metal gate extrusion. In further embodiments, dielectric fins mayinclude a tri-layer composition formed by alternating depositionprocesses (e.g., a first ALD process followed by an FCVD process, whichis followed by a second ALD process) for improved fabrication efficiencyand etching selectivity.

In one aspect, the present disclosure provides a semiconductor structurethat includes semiconductor fins protruding out of a substrate,dielectric fins protruding out of the substrate and disposed among thesemiconductor fins, where the dielectric fins include a first dielectricmaterial layer, a second dielectric material layer disposed over thefirst dielectric material layer, and a third dielectric material layerdisposed over the second dielectric material layer, and gate stacksdisposed over the semiconductor fins and the dielectric fins. In someembodiments, the first and second dielectric material layers havedifferent compositions, and the first and the third dielectric materiallayers have the same compositions.

In some embodiments, the first dielectric material layer includes anitrogen-containing material, and wherein the second dielectric materiallayer includes an oxygen-containing material.

In some embodiments, a width of the second dielectric material layer anda width of the third dielectric material layer both span betweensidewalls of the first dielectric material layer.

In some embodiments, sidewalls of the first dielectric material layercontacts sidewalls of both the second and the third dielectric materiallayers.

In some embodiments, the dielectric fins include a first dielectric finand a second dielectric fin, where the first dielectric fin includes thefirst dielectric material layer and is free of the second and the thirddielectric material layers, and the second dielectric fin includes thefirst, the second, and the third dielectric material layers. In furtherembodiments, the semiconductor fins are oriented lengthwise in a firstdirection, and the first and the second dielectric fins are orientedlengthwise in the first direction, and the dielectric fins furtherinclude a third dielectric fin oriented lengthwise in a second directionorthogonal to the first direction.

In some embodiments, the semiconductor structure further includes gatespacers disposed along sidewalls of the gate stacks, where the gatespacers are different from the first and the third dielectric materiallayers in composition.

In some embodiments, the semiconductor structure further includes hybridfins protruding out of the substrate and disposed among thesemiconductor fins and the dielectric fins, where a first portion of thehybrid fins and the third dielectric material layer of the dielectricfins are the same in composition and a second portion of the hybrid finsand the semiconductor fins are the same in composition. In someembodiments, sidewalls of the first portion and the second portion arecontinuous. In further embodiments, a bottom surface of the firstportion of the hybrid fins contacts the second portion of the hybridfins.

In another aspect, the present disclosure provides a method thatincludes forming a semiconductor fin structure over a substrate, fillingthe trenches with a first dielectric material layer and a seconddielectric material layer over the first dielectric material layer,where the second dielectric material layer including a compositiondifferent from the first dielectric material layer, resulting in adielectric fin structure having a plurality of dielectric fins, removinga portion of the second dielectric material layer to form a firstrecess, after the removing of the portion of the second dielectricmaterial layer, removing portions of the semiconductor fins, resultingin a second recess formed in portions of the semiconductor fins, fillingthe first and the second recesses with a third dielectric materiallayer, where the third dielectric material layer includes a compositionthe same as the first dielectric material layer, and forming gate stacksover the semiconductor fins and the dielectric fins. In someembodiments, the semiconductor fin structure includes a plurality ofsemiconductor fins and defines trenches among the semiconductor fins.

In some embodiments, filling the trenches includes performing an atomiclayer deposition (ALD) process to deposit the first dielectric materiallayer in the trenches, and depositing the second dielectric materiallayer over the first dielectric material layer to fill the trenches,where the depositing is implemented by a flowable chemical vapordeposition (FCVD) process. In further embodiments, the trenches includea first trench having a first width and a second trench having a secondwidth greater than the first width, where the performing of the ALDprocess includes depositing the first dielectric material layer tocompletely fill the first trench, and the depositing of the seconddielectric material layer includes depositing the second dielectricmaterial layer in the second trench.

In some embodiments, the filling of the first and the second recessesincludes performing an ALD process.

In some embodiments, the removing of the portion of the semiconductorfins exposes the substrate in the second recess, and the filling of thesecond recess forms a dielectric fin on the substrate.

In some embodiments, the removing of the portion of the semiconductorfins exposes the semiconductor fins in the second recess, and thefilling of the second recess forms a dielectric fin on the semiconductorfins.

In some embodiments, the method further includes performing a firstchemical mechanical polishing (CMP) process to the second dielectricmaterial layer after the filling of the trenches and performing a secondCMP process to the third dielectric material layer after the filling ofthe first and the second recesses.

In yet another aspect, the present disclosure provides a semiconductorstructure that includes first fins disposed on a substrate and orientedlengthwise along a first direction, where the first fins include asemiconductor material, second fins disposed among the first fins andoriented lengthwise along the first direction, where the second finsinclude a first dielectric material layer, third fins disposed among thefirst fins and the second fins and oriented lengthwise along the firstdirection, and gate stacks disposed over the first, the second, and thethird fins, the gate stacks being oriented lengthwise along a seconddirection orthogonal to the first direction. In some embodiments, afirst portion of each of the third fins includes the semiconductormaterial and a second portion of each of the third fins includes asecond dielectric material layer having the same composition as thefirst dielectric material layer.

In some embodiments, the second fins further include a third dielectricmaterial layer disposed over the first dielectric material layer and afourth dielectric material layer disposed over the third dielectricmaterial layer, where the third dielectric material layer is differentfrom the first dielectric material layer in composition and the fourthdielectric material layer is the same as the first dielectric materiallayer in composition.

In some embodiments, sidewalls of the first portion of each of the thirdfins are coplanar with sidewalls of the second portion of the each ofthe third fins along the first direction.

In some embodiments, a bottom surface of the second portion of each ofthe third fins is below a bottom surface of each of the second fins.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure comprising:semiconductor fins protruding out of a substrate; dielectric finsprotruding out of the substrate and disposed among the semiconductorfins, the dielectric fins including a first dielectric material layer, asecond dielectric material layer disposed over the first dielectricmaterial layer, and a third dielectric material layer disposed over thesecond dielectric material layer, wherein the first and seconddielectric material layers have different compositions, and wherein thefirst and the third dielectric material layers have the samecompositions; and gate stacks disposed over the semiconductor fins andthe dielectric fins.
 2. The semiconductor structure of claim 1, whereinthe first dielectric material layer includes a nitrogen-containingmaterial, and wherein the second dielectric material layer includes anoxygen-containing material.
 3. The semiconductor structure of claim 1,wherein a width of the second dielectric material layer and a width ofthe third dielectric material layer both span between sidewalls of thefirst dielectric material layer.
 4. The semiconductor structure of claim1, wherein sidewalls of the first dielectric material layer contactssidewalls of both the second and the third dielectric material layers.5. The semiconductor structure of claim 1, wherein the dielectric finsinclude a first dielectric fin and a second dielectric fin, wherein thefirst dielectric fin includes the first dielectric material layer and isfree of the second and the third dielectric material layers, and whereinthe second dielectric fin includes the first, the second, and the thirddielectric material layers.
 6. The semiconductor structure of claim 5,the semiconductor fins being oriented lengthwise in a first direction,and the first and the second dielectric fins being oriented lengthwisein the first direction, wherein the dielectric fins further include athird dielectric fin oriented lengthwise in a second directionorthogonal to the first direction.
 7. The semiconductor structure ofclaim 1, further comprising gate spacers disposed along sidewalls of thegate stacks, wherein the gate spacers are different from the first andthe third dielectric material layers in composition.
 8. Thesemiconductor structure of claim 1, further comprising hybrid finsprotruding out of the substrate and disposed among the semiconductorfins and the dielectric fins, wherein a first portion of the hybrid finsand the third dielectric material layer of the dielectric fins are thesame in composition, wherein a second portion of the hybrid fins and thesemiconductor fins are the same in composition, and wherein sidewalls ofthe first portion and the second portion are continuous.
 9. Thesemiconductor structure of claim 8, wherein a bottom surface of thefirst portion of the hybrid fins contacts the second portion of thehybrid fins.
 10. A semiconductor structure comprising: first finsdisposed on a substrate and oriented lengthwise along a first direction,wherein the first fins include a semiconductor material; second finsdisposed among the first fins and oriented lengthwise along the firstdirection, wherein the second fins include a first dielectric materiallayer; third fins disposed among the first fins and the second fins andoriented lengthwise along the first direction, wherein a first portionof each of the third fins includes the semiconductor material and asecond portion of each of the third fins includes a second dielectricmaterial layer having the same composition as the first dielectricmaterial layer; and gate stacks disposed over the first, the second, andthe third fins, the gate stacks being oriented lengthwise along a seconddirection orthogonal to the first direction.
 11. The semiconductorstructure of claim 10, wherein the second fins further include a thirddielectric material layer disposed over the first dielectric materiallayer and a fourth dielectric material layer disposed over the thirddielectric material layer, the third dielectric material layer beingdifferent from the first dielectric material layer in composition andthe fourth dielectric material layer being the same as the firstdielectric material layer in composition.
 12. The semiconductorstructure of claim 10, wherein sidewalls of the first portion of each ofthe third fins are coplanar with sidewalls of the second portion of theeach of the third fins along the first direction.
 13. The semiconductorstructure of claim 10, wherein a bottom surface of the second portion ofeach of the third fins is below a bottom surface of each of the secondfins.
 14. A semiconductor structure comprising: a semiconductor finprotruding from a substrate and oriented lengthwise along a firstdirection, wherein the semiconductor fin includes a semiconductor layer;a hybrid fin protruding from the substrate and oriented parallel to thesemiconductor fin, wherein the hybrid fin includes the semiconductorlayer and a first dielectric layer disposed over the semiconductorlayer; a first dielectric fin protruding from the substrate and orientedparallel to the semiconductor fin, wherein the first dielectric finincluding the first dielectric layer; a second dielectric fin protrudingfrom the substrate and oriented parallel to the semiconductor fin,wherein the second dielectric fin includes a second dielectric layerdisposed over the first dielectric layer, wherein the second dielectriclayer is different from the first dielectric layer in composition, andwherein the first dielectric fin is free of the second dielectric layer;and conductive gate stacks disposed over the semiconductor fins, thefirst dielectric fin, and the second dielectric fin and orientedlengthwise along a second direction normal to the first direction. 15.The semiconductor structure of claim 14, wherein the first dielectricfin is defined by a first width along the second direction and thesecond dielectric fin is defined by a second width along the seconddirection, and wherein the first width is less than the second width.16. The semiconductor structure of claim 14, further comprising a thirddielectric fin protruding from the substrate and oriented parallel tothe conductive gate stacks, wherein the third dielectric fin includesthe second dielectric layer embedded in the first dielectric layer. 17.The semiconductor structure of claim 16, wherein portions of the hybridfin in contact with the third dielectric fin include the firstdielectric layer, and wherein remaining portions of the hybrid fin arefree of the first dielectric layer.
 18. The semiconductor structure ofclaim 17, wherein the semiconductor layer and the third dielectric findefine sidewall surfaces of the first dielectric layer in the hybridfin.
 19. The semiconductor structure of claim 14, wherein the firstdielectric layer is in contact with a top surface and sidewall surfacesof the second dielectric layer in the second dielectric fin.
 20. Thesemiconductor structure of claim 14, wherein the first dielectric layerincludes a nitrogen-containing material, and wherein the seconddielectric layer includes an oxygen-containing material.